Wafers that are currently used in the semiconductor industry are typically placed on a fixture during a manufacturing process to allow the wafer to be positioned and aligned properly so that a manufacturing procedure or testing procedure may be conducted thereon. For example, often the wafer is tooled to meet certain predetermined specifications as part of the overall manufacturing process and after manufacture, the wafer is tested to see if the wafer meets certain guidelines, e.g., quality control and performance standards.
Wafer holding chucks have taken various forms in the prior art, including the use of a vacuum holding chuck apparatus for chucking an article like a plate, a box, or a wafer. In a simple embodiment, a vacuum holding chuck includes a generally planar surface having a central opening which is connected to a vacuum source, by either an external tube or by disposing at least one internal vacuum passageway within the chuck itself, whereby the vacuum source is connected to the internal passageway leading to a vacuum port. The article (e.g., wafer) is placed on the planar support surface and when the vacuum apparatus is actuated, the vacuum evacuates the air resulting in the wafer being held on the chuck securely. One variant of this type of wafer holding chuck is an apparatus having a plurality of vacuum ports dispersed throughout the planar support surface which receives the article. All of the vacuum ports are connected to the vacuum source so that when actuated, the article is drawn toward and held against the planar support surface by the vacuum. The rationale is that by increasing the number of vacuum ports, the multiple vacuum ports act on the article in multiple locations causing the article to be securely held in place.
Additionally, other known wafer holding chucks secure the article by using a number of suction cups pressed against a predetermined surface area of the article to be chucked and the air in the suction cups is evacuated, whereby the article is chucked by the suction created by the vacuum chuck apparatus.
While there are several apparatuses and methods of chucking an article, the success achieved by each apparatus in securely holding the article against the planar support surface has not been entirely satisfactory. This is especially true for wafer holding chucks which are intended to hold wafers and particularly semiconductor wafers during a manufacturing process and/or testing procedure. One of the associated disadvantages of the prior chucks is that in many instances the chucks do not provide an apparatus which securely holds the article (e.g, wafer) on the chuck very well. In chucks having an inadequate number of vacuum ports or inadequate vacuum distribution over the wafer surface to be chucked, the wafer is not sufficiently held in place so as to prevent undesired movement thereof, which would encumber and likely render ineffective either a manufacturing procedure or a testing procedure of the wafer. This undesired movement of the wafer on the planar support surface results from vibration or shaking of the wafer during or more of the above-listed events.
Another of the associated disadvantages of prior wafer holding chucks is that typically, the chucks have a single side for receiving the wafer with this single side including the planar support surface to which the wafer is applied. Wafers of varying diameter are placed on the planar support surface and most chucks are not specifically designed to accommodate wafers of varying diameters but instead the wafers are held in place by placing the wafer over a number of vacuum ports and there are no guides provided to properly align the wafer.
Another disadvantage is that improper placement of the wafer on the planar support surface or improper chucking of the wafer can lead to warping of the wafer itself. If the air is improperly evacuated from the chuck and the wafer thereon, the tendency for the wafer to warp is greatly increased resulting in less precision in the manufacturing and testing of the wafer. In other words, when the wafer is placed on the planar support surface, there is an amount of air which exists between the bottom surface of the wafer and the planar support surface. When the vacuum is applied to the chuck, this pocket of air will cause the wafer to warp or bulge due to the trapped air underneath this portion of the wafer during evacuation of the surrounding air by the vacuum.
Other wafer holding chucks have complicated designs which utilize a number of clamping devices to pinch the edges of the wafer to the planar support surface to securely position the wafer thereon. These chucks have the associated disadvantage that they offer a more complex design involving additional components which results in a more costly and complex apparatus and a more time consuming procedure to securely hold the wafer to the chuck during the desired process or procedure.